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If what users on, say Twitter say constitute it “saying something” then perhaps it should remove the standard disclaimer of how the opinions expressed thereon are that of their users, and not their own, and be held personally liable for what is posted on there.Why? Hacker News, or Twitter, can say things for itself, and it can also host other people's opinions. There is no collision there. Twitter has Free Speech rights, and is responsible for, whatever it says itself. Twitter also has the Free Speech right to support, or not, anything it likes since it is in no way quasi-governmental. It doesn't owe anyone a soap box. And there is no reason it should be held liable for what users say, the users who say those things should be held liable.
>When it suit these platforms, they claim that the opinions are of their users and not their own
The law, and common sense as well is clear. Words of their users are not, in fact, theirs. The only thing regular law gives them is protection from not being completely perfect in their attempts at exercising their own Free Speech vs other people on their own property, rather than having to use Common Carrier all-or-nothing. But they could ban whomever they liked regardless.
>yet when it otherwise suit them, they claim ownership.
Specify. They own their own words and their own resources, and necessarily users must offer them at least a limited non-exclusive license for reproduction due to copyright. That is a fair tradeoff offer for what their users gain, and everyone may accept, or not.
Which ones "claim ownership" of other people's words and how? They don't need any ownership for bans, because nobody is entitled to their support.